Communication system



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S. B. WILLIAMS COMMUNI CATION SYSTEM Filed NOV. 26, 1941 10 SheetsSheet 6 S/FE-IIIHI" //V 1 15 N TOR By s. 13W. L IAMS A T TOR/VE Y Feb. 23, 1943. s w s 2,311,800

COMMUNICATION SYSTEM Filed Nov. 26, 1941 10 Sheets-Sheet 7 IIHI' SECOND SELECTOR //V [/5 N TOR By B. W/LL/AMS "61 1 A 7' TORNE V Feb. 23,1943.

5. B. WILLIAMS COMMUNICA-TION SYSTEM Filed Nov. 26, 1941 10 Sheets-Sheet 8 l/V VENTOR s. B. WILLIAMS A T TORNE Y s. B. WILLIAMS COMMUNICATION SYSTEM Filed NOV. 26, 1941 10 Sheets-Sheet 9 w l E/V TOR S. B. W/LL IAMS ATTOPNEV Feb. 23, 1943. s. B. WILLIAMS COMMUNICATION SYSTEM- 1o Sheets-Shet '10 Fil ed Nov. 26. 1941 INVENTOR S. B. W/LL/AMS ATTORNEY Patented Feb. 23, 1943 COMMUNICATION SYSTEM Samuel B. Williams, Brooklyn, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 26, 1941, Serial No. 420,445

6 Claims.

This invention relates to selective switches and particularly to switching devices useful in telephone systems of a type through which an incoming line may be extended to an idle outgoing line of any one of a number of groups of such lines by directive and automatic action.

The object of the invention is to adapt the now well-known crossbar type of switch to stepby-step operation. Applicant is aware that this object in general has been achieved by others but he has devised a new arrangement which has many economical and operating advantages whereby the present invention embodies a step forward in the art.

Broadly stated the present invention resides in the use of a field of sets of permanently paired contacts coordinately arranged with selecting magnets for the rows of contacts in one direction and holding magnets for the rows of contacts in another direction. Incoming lines appear in a part of the field and outgoing lines appear in another part of the field. The switch is operated by having a simple stepper auxiliary thereto responsive to impulses incoming over said incoming lines to selectively operate a selecting magnet corresponding to a wanted group of outgoing lines. The operation of the selected selecting magnet will establish a testing circuit for the outgoing lines of the said selected group whereupon a set of contacts is operated through the automatic operation of an appropriate holding magnet. This will result in a connection of the selected outgoing line to a link extending into the field of said incoming lines, whereupon the originally operated selecting magnet is released and another selecting magnet corresponding to the connected link automatically operated to extend the link to the calling incoming line.

A feature of the invention is an arrangement whereby the links are multipled in one coordinate direction in one field of the said switch and are multipled in another coordinate direction in another field of the said switch.

Another feature resides in the means whereby after the first selecting magnet of the switch is directively operated a sequence of other operations is caused to automatically follow including the operation of a holding magnet corresponding to an idle trunk in the selected group of trunks. the release of the first selecting magnet and the operation of another selecting magnet for connecting the calling line to a now established connection between a called line and an interfield link.

Another feature is the method of operating a crossbar switch by impulses incoming over a calling line which includes the steps of firstly directively and automatically establishing a connection between an idle outgoing line of a selected group and an interfield link, secondly releasing the means for preparing for the said first step, and thirdly automatically establishing a connection between the said calling line and the said interfield link.

Other features will appear in the following description.

The drawings consist of ten sheets of circuit diagram which, when placed together as indi cated in Fig. 6, will form a complete circuit diagram of a telephone switching system embodying the present invention.

Fig. 1 shows primary line switching arrangements;

Fig. 2 shows secondary line switching arrange- 20 ments;

Figs. 3, 3A and 3B show the circuits of a first selector;

Fig. 3 shows the arrangement of the crossbar switch comprising a group of such first selectors, Fig. 3A shows the register circuits and Fig. 3B shows the common control circuit;

Figs. 4 and 4A show the arrangements for a second selector, this being. a variation of the arrangement used in Figs. 3, 3A and 33;

Fig. 4 shows the crossbar switch used as a group of second selectors and Fig. 4A shows the register and common control circuits used therefor;

Figs. 5, 5A and 5B show the connector circuit arrangements;

Fig. -5 shows the crossbar switch used for a group of connectors, Fig. 5A shows the connector circuits comprising the apparatus individual to the incoming trunks and Fig. 5B shows the common control circuits operated thereby.

Fig. 1 is a schematic representation of a group of primary line switches and Fig. 2 is a schematic representation of a group of secondary line switches. The four contact sets to the left represent one primary line switch and the four contacts sets to the right represent another. Each incoming line occupies a vertical row and each link to a secondary line switch occupies a horizontal row. Thus the line from station I occupies the vertical row represented by contact sets 2 and 3 and has individual to it the hold magnet 4, the cut-off relay 5 and the line relay 6. This line represents the first and line 1 represents the last of the group of lines served by 65 this one switch. Similarly line 8 represents the tact of relay 35.

first and line 9 represents the last of a group of lines served by the other of said switches.

A trunk I3, served by the contact sets 2, I9, II and I2 represents the first and a trunk I4 served by the contact sets 3, I5, I6 and I! represents the last of a group of trunks served by the group of switches represented schematically in this Fig. 1.

The arrangement in Fig. 2 is similar to the arrangement in Fig. 1. The trunks from Fig. 1 appear in the verticals of Fig. 2. Thus trunk I3 having contact sets I8 and I9 and hold magnet and line relay 2| individual thereto represents the first and trunk I4 having contact sets 22 and 23 and hold magnet 24 and line relay 25 individual thereto represents the last of a group of trunks served by the secondary line switch represented by the contact sets I8, I9, 22 and 23. The trunks 26 and 21 represent the first and the last of a group of trunks served by the secondary line switch represented by the contact sets 28, 29, and 3 I. These trunks come from another group of line switches similar to those shown in Fig. 1. The outgoing trunks 32, served by the contact sets I8, 22, 28 and 30 and 33 served by the contact sets I9, 23, 29 and 3I represent the first and last of a group of trunks outgoing from the secondary line switches of Fig. 2.

A call from station I results in the operation of the line relay 6. This connects ground to a common wire leading to the left-hand winding of relay 34 which is individual to the line switch represented by the contact sets 2, 3, I0 and I5. When relay 34 operates it closes a locking circuit for itself through its right-hand winding, its

front contact and right-hand armature, the left-hand armature and back contact of relay 35 and the winding of relay 36 resulting in the holding of relay 34 and the operation of relay 36. Relay 36 opens the circuit for the left-hand winding of relay 34 as well as the left-hand winding of all similar relays such as relay 31. This is a non-interfering circuit, there being one relay such as 34 or 31 for each group of lines that have access to the same group of primary-secondary trunks.

The operation of relay 36 operates relay 38 through the contacts of relay 39 and this then connects ground to the sleeve relays of the primary-secondary trunks. dicated by the non-operated condition of its associated sleeve relay extends this ground through its left-hand armature and back contact to operate its associated selecting magnets of the primary line switches. Those sleeve relays which are operated when this takes place are locked to ground from relay 38 to stabilize the operating condition for the selecting magnets.

When relay 38 operates, a circuit is closed for the operation of relay 39. Relay 38 is slow releasing and relay 39 is slow operating and due to these characteristics the selecting magnets of the switches will have suflicient time to operate and the select finegrs will have sufficient time to settle down. When relay 39 operates, ground is connected through the lefthand armature of relay '34 to the armature of the line relay 6 to cause the operation of the hold magnet 4. This results in the operation of a selected contact set and the connection therethrough of the line to the trunk.

Through the operation of the hold magnet 4 this ground is extended to the cut-off relay 5 which puts the line relay 6 from the line conductors. When relay 39 is operated it looks to a back con- The first idle trunk in- When thereafter relay 38 re- 75 leases relay 35 is operated and this relay now looks to a front contact of relay 36. However, relay 35 opens the circuit of relay 36 and when this relay releases, the control circuit is restored to normal.

When relay 38 operated, ground was connected through contacts of the vertical hold magnet (20, for instance) to operate the secondary line relay (2|, for instance). The operation of the secondary line switch circuit is the same as that of the primary line switch circuit except that no cut-off relay is required and the line relay is locked through a contact on the vertical hold magnet. This is to insure that the trunk from the primary line switch is not prematurely released. The line relay 2I also has a lower holding winding which is in series with the winding of the hold magnet 20. This insures that both the primary and secondary line switches are not prematurely released as the slow-releasing relay 40 can be made slow enough to hold the primary and secondary line switches until the first slow release relay of the first selector register circuit is operated and ground is connected to the sleeve conductor of the trunk from the secondary to the first selector.

A chain relay 4| is provided and is associated with the secondary control circuit which is operated in series contacts on the secondary sleeve relays 42 and 43. The operation of relay 4I causes the operation of all the primary sleeve relays 44 and 45 of all the primary-secondary trunks appearing before the particular group of outgoing trunks from the secondary line switch to the first selector.

Figs. 3, 3A and 3B show a 20-vertical crossbar switch arranged to provide for nine ZOO-point selectors, the outgoing trunks being disposed in ten levels of twenty trunks each. The first nine selector verticals are of the three-wire type providing access from any one of the nine selectors to the multiple. The ten three-wire horizontals multipled before the selector verticals are connected by relays such as 46 and 41 to ten six-wire trunk verticals. Four five-wire verticals are provided as trunk connectors.

Thus the trunk 32 from the secondary line switch appears in contact sets 48 and and has hold magnet 62 and relay 63 individual thereto. and the trunk 33 from the secondary line switch appears in contact sets 49 and 56 and has hold magnet 64 and relay 65 individual thereto. Trunk 32 represents the first and trunk 33 represents the last of the trunks incoming to this first selector switch.

The horizontal row of contact sets 48, 49, 50, 5I, 52 and 53 are under control of the select magnet 54 and the horizontal row of contact sets .55, 56, 51, 58, 59 and 60 are under control of the select magnet 6 I. These two rows represent the first and last rows of this first selector switch.

Contact sets 59, 5!, 51 and 58 represent means to connect a switch link to an outgoing trunk and each of said sets accommodates two trunks. The contact sets 48 and 49 represent means to connect an incoming trunk to a switch link and each accommodates a single link. The links appear in horizontal rows in the three-wire contact sets and in vertical rows in the six-wire contact sets. Thus link 66 appears in the contact sets 48 and 49 and in contact sets 50 and 51 where it is expanded by the relay 46 into two paths 6'! and 68. The contact sets 52 and 53 in the top horizontal row are used for testing purposes, the

sleeves of all outgoing trunks in that horizontal row appearing therein.

A register is provided for four or five selectors, but if the traific permits, one register may be used for all nine selectors, The registers are equipped with a stepping device which responds to dial pulses. After the dial pulses cease, the register is connected to the switch control circuit and the register causes the proper selecting magnet to be operated after which the four five-wire vertical magnets are operated to connect the sleeve of the twenty trunks n the selected level to the crosspoint test relays. These relays are likewise connected to the trunk vertical magnets. This trunk vertical has access to two trunks and both are made busy by the crosspoint test. The TK relay (such as relays 46 and 41) corresponding to the selected trunk vertical is operated, if necessary, to connect the corresponding three-wire horizontal before the selector verticals to the proper group of three contacts on the trunk verticals. The trunk vertical or hold magnet indicated by the crosspoint test is then operated and the selecting magnets and trunk test vertical magnets are released.

The crosspoint test relays indicate the proper selecting magnet to be operated corresponding to the trunk vertical magnet that has been operated, and after this selecting magnet is operated, the selector vertical magnet is operated, to connect the selector circuit to the trunk. At the same time, the release of the register is started. The switch control circuit is released immediately so as to be available to the mate register if a selecting operation is desired.

Ground on the sleeve of an incoming trunk, such as 32 will be extended through the normal contacts of the hold magnet 62, thence through a back contact of a group relay 69, to the winding of relay 63, which is operated thereby. The operation of this relay immediately energizes the first slow-release relay 18 of the register although the pulsing relay 'II is connected to the ring conductor by relay 63. The circuit for the immediate operation of relay is from battery 45 winding of magnet 12, winding of relay 18, upper armature and back contact of relay 13, lower armature and back contact of group relay 69,

front contact and armature 5 of relay 63 to' ground. The operation of relay 19 operates relay 69 and locks relay 63 through its armature 4. The operation of relay 69 prevents any other relays such as 63 and 65 from operating and connects ground to the incoming selector sleeve conductors of all the selectors having access to the register circuit. The operation of relay Il holds relay l8 operated after relay 69 has opened the original energizing circuit of relay '10.

The dial pulses release relay H intermittently. In this circuit relay H is equivalent to the line relay of the well-known step-by-step controlling circuit, relay 1D is equivalent to the first slow-releasing relay and relay [5 is equivalent to the second slow-releasing relay. Relay 1| responds to the line interruptions, relay 10 5 holds until relay II is released for more than a given time and relay I4 responds to a train of I impulses as a whole. Magnet I5 in series with' the upper winding of relay [4 responds to each impulse separately and magnet 12 operates dur- 70 ing the periods when magnet 15 is not energized. Magnets 12 and 15 and the rest of the apparatus shown in the broken line rectangle represent a single relay structure having on or more reed armatures, a plurality of pole-pieces anda pluthe 0, 1, 2-9 plan used in other systems.

rality of energizing coils whereby the functions of a plurality of interconnecting circuits may be accomplished. The device is an electromechanical equivalent of a chain of counting relays and is clearly described in an application Serial No. 389,322, filed April 19, 1941, by George R. Stibitz. The conductors 16 represent the ten conductors used for the ten digits 1 to 0.

The intermittent operation of relay 1| then causes the stepper to advance. It should be noted that when magnet 15 of the stepper is energized, a contact is closed to energize the lower winding of relay 14. The purpose of this is to reduce the time release requirements of relay 14. The release of this relay at the end of a train of pulses closes a circuit to operate relay 18 in a circuit from battery, winding of relay 18, back contact and armature l of relay 11, back contact and armature of relay 14, a contact in the stepper, front contact and armature 2 of relay [9, armature 2 and back contact of relay 13, front contact and armature 3 of relay 19 to ground.

By way of example, let it be assumed that the stepper has been set by the digit 0. Thereupon a circuit may be traced. from ground, armature 3 and front contact of relay l8, armature 3 and back contact of relay 19, armature 4 and front contact of relay 18, to 0 wire of the bundle designated 16, to the winding of selecting magnet 54 to battery. This selecting magnet corresponds to the digit dialled and indicates the level or group of trunks desired. The operation of the selecting magnet 54 closes a circuit from ground, armature 3 and. front contact of relay l8, armature and front contact of selecting magnet 54, winding of relay to battery. Relay 80 connects ground, through its front contact and armature I, through armature l and back contact of relay 19, to the winding of magnets 8! and 82 causing them to operate. The operation of these magnets through the operation of contact sets 52 and 53 connects the sleeves of the trunks of the selected group through the back contacts of relays such as 83 and 84 to the windings of the crosspoint test relays such as 85, 86, 81 and 88.

The numbering plan follows the usual stepby-step numbering plan of 1, 2, 3-0 instead of I There are two sets of ten relays involved in the crosspoint test. Relays such as 81 and 85 make the crosspoint test for the trunk associated with that portion of the link coming from the back contacts of relays such as 46 and 41 and relays such as 88 and 86 make the crosspoint test for the trunk associated with that portion of the link coming from the front contacts of relays such as 46 and 41. If outgoing trunks 9| to 94 represent the first and last pairs or the first, second, nineteenth and twentieth trunks of a group then relay 8'! will test trunk 9|, relay 88 will test trunk 92, relay 85 will test trunk 93 and relay 86 will test trunk 94. Relays 81 and 88 represent the first pair of relays 85 and 86 represent the last pair of the group of these test relays. When the test relays indicate an even numbered trunk, such as 92 and 94, to be selected, then the relay such as 46 and 41 associated with the trunk vertical is to be operated. The sleeve windings of the relays 85 to 88 are connected to the trunk sleeve conductors through back contacts of relays 83 and 84. These relays together with relay 89 are slow to operate to allow time for the operation of relays 85 to '88 as determined by the condition of the trunk sleeve.

Relays v85 to 88 will also be operated due to their connection to the sleeve conductors of the horizontal links. Thus the sleeve of link 66 may be traced in series through the right-hand windings of relays 86 and 85 and the sleeve of the other link shown may .be traced through the right-hand windings of relays 88 and 81. Windings on the relays 85 to 88 for a given crosspoint are connected in series so that if the relays 83 and 84 ar operated both relays will be operated to indicate that the crosspoint is busy. Relays 83, 84 and 89 open the energizing leads from the windings of relays 85 to 88 and they look in the chain from the front contact of armature 4 of relay 84. It will be noted that the back contacts of armature 2 of relays 88 and 88 connect with relays 46 and 41. Thus if a crosspoint test indicates that a trunk associated with the front contacts of a link relay 46 or 4'! is chosen the proper .one of such link relays will be operated over this path. When relay 89 finally operates, a circuit is closed through the contacts of the test relays to the selected hold magnet 98 or 95 which operates and extends this ground through contacts of the relays '88 and 88 and .the contact of relay 96 to operate relay l9. Relays 88 and 86 represent a chain of ten relays so that upon the operation of relay 89 a circuit may be traced from ground, armature 2 and back contact of relay 9i, armature I and front contact of relay 89, armature 4 and front contact of relay 86,

assuming relay 86 to 'be operated, thence in a chain through the armature 4 and front contacts of all other similar busy relays in a chain to armature 4 and back contact of relay 88 which will now be assumed to be non-operated and representing by that state an available trunk, thence to the winding of hold magnet 96 which is thereupon operated. Through the operation of magnet 98 the ground for its operation is extended over the front contact and armature l of magnet 89 to the back contact and armature 5 of relay 88, thence in a chain over the front contacts and armatures 5 of the assumed operated relays of this chain to the armature 5 of relay 86, thence over armature 2 and front contact of relay 89, the winding of relay '59 to battery. This results in the operation of relay l9.

Relay 19 disconnects ground from the stepper and the selecting magnet 54 releases, in turn releasing relay 88 and the test vertical magnets 8! and 82.

As soon as relay 88 releases relay 96 is operated and ground is connected to a series circuit through contacts of relays 85 to 88 to operate the proper selecting magnet corresponding to the operated trunk vertical or holding magnet. Thus ground may now be traced from armature 2 and front contact of relay 96, armature l and front contact of relay 86, thence in a chain through armature l and front contact of similar relays in a chain to armature I and back contact of relay 88, now assumed to be not operated, to the winding of selecting magnet 6|.

Relay 88 again operates through the armature and contact of magnet 6| and ground is connected through the contacts of relays T8 and 63 to operate the hold magnet 62. This circuit may be traced from battery winding of hold magnet 82, armature 3 and front contact of relay 63, front contact and armature 2 of Trelay 78, front contact and armature l of relay [9, armature I and front contact of relay 80, front contact and armature 3 of relay [8 to ground. As this ground passes through the register circuit, relay T3 is operated to open the circuit of the first slow releasing relay l0 and remove ground which has been holding relay 13 operated, thus releasing the switch control circuit immediately. Relay 16 is slow to release and holds ground on the sleeve conductor of the selector circuit to give time for the selector beyond to connect ground to the sleeve conductor. The hold magnet 62 in operating extends the sleeve conductor of the selected trunk to the sleeve conductor of the incoming trunk.

If all the relays to 88 operate, indicating that all the crosspoints are busy, the all-trunksbusy relay 98 operates and relay 9'! starts to release. The operation of relay 98 releases relays 85 to 88 and 89. Relay 9'! which is somewhat slow to release, restores the operating circuit of relay 89 and the locking circuit of relays 85 to 88. When relay 89 released, all the relays 85 to 88 corresponding to the busy links operated but at least one of them will not be operated because there are only nine selectors for the ten horizontals. The non-operated relay of the group 83 and 88 causes the operation of the proper selecting magnet because the operation of relay '98 operated relay 19 to release the trunk test vertical magnets and the selecting magnets and relays 86 and 99 operate to operate the selector vertical magnet.

Connection through the selector vertical is now extended through back contacts on the trunk vertical or holding magnet 98 to the busy tone circuit. Relay 99 is operated to guard the release and busy tone is connected to the tip conductor. When the calling subscriber releases relay 99 restores and the selector is entirely released.

Figs. 4 and 4A represent a second selector. This might be identical with the first selector of Figs. 3, 3A and 3B, but is shown in somewhat difierent form. The fundamental plan of operation is the same but the arrangement is much simpler. These figures show a 20-vertical crossbar switch which provides eight selectors having access to a common IOU-point multiple, the trunks being arranged in ten levels of ten trunks each. The selectors are divided into two groups of four, each group being served with a register which responds to a single digit or full of the dial. After this digit has been registered, connection is made with a common switch control circuit which first operates the selecting magnet corresponding to the level indicated by the digit dialled to connect the sleeve conductors of the trunks on that level to the crosspoint test relays. These relays are also connected to the links. As soon as the crosspoint test is made, the selected trunk is made busy through the test verticals and the proper trunk vertical magnet is operated thus connecting the selected trunk to the selected link which appears before all of the selector verticals. The selecting magnets are then released and reoperated in accordance with the link indicated by the operated trunk vertical magnet. The selector vertical magnet of the articular selector to which at this time the test circuit is connected through the register circuit is operated. Coincident with this operation, the stepping device which responded to the dial pulses is started to reset and the switch control circuit is released from the register circuit so as to be available to the mate register circuit as soon as possible. The register circuit releases from the selector circuit under control of the usual slow-release relay so as to hold over during the time that the succeeding register circuit is attached to the selected out trunk.

As shown the incoming-trunks BI and I represent the first and the last of a group of incoming trunks served by this switch. Trunk 9|, as its number indicates may come from the preceding first selector in Fig. 3. Trunk I00 may come from the same first selector or from some other first selector. The contact sets IM and I02 represent the first and last contact sets individual to the trunk 9I and under control of the selector vertical or holding magnet I05. Likewise the contact sets I03 and I04 represent the first and last contact sets individual to the trunk I00 and magnet I05. Contact sets IOI, I03, I01, I08, I09

and H0 in the upper horizontal row are under control of the selecting magnet II I and likewise contact sets I02, I04, H2, H3, H4 and H5 in the lower horizontal row are under control of the selecting magnet H5. A first link is served by the incoming trunk contact sets NH and I03 and by the outgoing trunk contact sets I01 and H2 and a last link is served by the incoming trunk contact sets I02 and I04 by the outgoing trunk contact sets I00 and H3. The contact sets I09, H0, H4 and H5 represent means to connect the sleeves of the trunks of a selected level or group to the crosspoint test relays.

The numbering plan here used is the usual step-by-step plan starting with 1 and ending with 0 and representing one and ten impulses respectively. In the first selector of Fig. 3 the levels or groups started as l at the bottom and advanced to 0 at the top. In the present case the levels start at I at the top and advance to 0 at the bottom. In other words the sequence of the numbering from 1 to 0 reads downwardly and from left to right. Thus the outgoing trunks from contact sets I01, I08, H2 and H3 will be numbers 11, 10, 01 and 00 respectively.

The detailed operation of this second selector is as follows:

Ground on the incoming sleeve of the selector circuit operates a relay such as H1 individual thereto. This circuit may be traced from battery winding of relay H1, back contact and armature I of relay H8, back contact and armature I of selector vertical or holding magnet I05 to the sleeve wire of the incoming trunk 9|. Through the operation of relay H1 ground is extended through armature 3 and front contact of relay H1, back contact and armature 3 of relay H8 through the winding of first slow releasing relay H9 to battery. .As soon as relay H9 operates relay H8 operates in a circuit from ground, front contact and armature 2 of relay H9, winding of relay H8 to battery and in .parallel therewith through armature 4 and contact of relay I I1 for a locking circuit therefor. Relay I I8 opens the original energizing circuit of relay H1 but through its front contacts places ground on the sleeve conductors of all other incoming trunks of this group having access to the same register. Relay H1 connects the tip and ring conductors through its armatures 5 and 2, respec tively, to the windings of line relay I20, line relay I operates and through its armature and front contact holds the first slow releasing relay H9 operated.

The line relay I20 responds to the dial pulses and operates relay I2I in series with the stepping magnet I22. Relay I2I is the usual second slow-releasing relay and therefore responds to the chain of impulses as they hold while the stepping magnet I22 responds to each separate impulse, the stepping magnet I22 steps the brush I23 to a contact corresponding with the number of impulses in chain and grounds one of a bundle of ten conductors as corresponding to one of the ten digits. These conductors are shown only in part and are indicated by a single line running through the front contact and armature of relay I24 which represents ten similar front contact and armature combinations likewise through the armature I and back contact of relay I25 and the front contact and armature I of relay I26 which also represent ten similar contact and armature combinations. This same combination may be traced to the back contacts of armature 5 of the ten crosspoint test relays such as I21 and I28. The back contacts of armature 4 of the trunk vertical or holding magnets such as I29 and I30 and to the'windings of selecting magnets such as III and H6. The numbering of these holding and selecting magnets and crosspoint relays will correspond to the numbering of the leads coming from the switch wiper When the pulses cease relay I2I releases and ground from the step off-normal contact I3I will be extended through the armature and back contact of relay I2I, back contact and armature I of relay I32, winding of relay I33 to battery. Relay I33 responds if the mate relay I32 has not been operated. There is an interlocking circuit between relays I32 and I33 corresponding to the two registers to lock out one or the other when the switch control circuit is engaged. When relay I33 operates relay I24 is energized and the ten conductors from the contacts of the step are connected through front contacts of a relay I24 and back contacts of relay I25 to the selecting magnets. The selecting magnet corresponding to the digit dialled is then operated and this in turn will cause the operation of relay I34.- The operation of relay I34 extends ground from armature and front contact of this relay through the back contact and armature 3 of relay I25 to the windings of trunk test vertical or holding magnets I35 and I35. Both these magnets operate and extend the ground for their operation through their front contacts and armatures to the winding of relay I31 which also operates at this time.

As soon as the contacts on the verticals controlled by these two holding magnets operate the sleeve conductor of the trunks in the desired group designated by the particular selecting magnet operated are connected to the relay windings of the crosspoint test relays I21and I28 through back contacts of relay I31. The sleeve conductors of the links connected to the armatures of trunk vertical magnets I29 and I30 are connected to the corresponding relays I21 and I23 through back contacts of relay I38. Relays I31 and I38 are slow enough in operation to permit the crosspoint test relays to operate in accordance with the busy crosspoints in the trunk multiple. As soon as relays I31 and I38 operate the crosspoint test relays are locked in to designate a position idle crosspoint and the sleeve conductor of the selected idle trunk is connected to ground through contacts of relay I31 and the particular crosspoint test relay which indicates an idle crosspoint. Assuming crosspoint test relay I28 to remain unoperated then a circuit may be traced from ground, armature 6 and front contact of relay I33, armature I and front contact of relay I31, armature I and front contact of relay I21 and thence through the armature I and front contacts of the other crosspoint test relay to armature I of relay I28 which is now assumed to be the first idle one of these relays thence through the back contact of this armature to the sleeve of the outgoing trunk served by contact set II3. Ground may be also traced from ground, arma ture 6 and front contact of relay I33 through armature 2 and front contact of relay I31, armature 2 and front contact of relay I21. thence through similar armature in contact arrangements on the other crosspoint test relays to armature 2 and back contact of relay I28 thence to the winding of the test vertical or holding magnet I to battery. The operation of magnet I3B. causes the connection of an idle link to the selected. idle trunk assuming that the lower horizontal, row of contacts have been selected by the selecting magnet III;v then contact set II3 will be operated. The operation of. magnet I33 extends the ground for its operation through its front contact in armature Ito a circuit which may be traced through the back contact and armature 4 of crosspoint test relay I28. thence in a series circuit. through the front contacts and armatures 4. of the other operated crosspoint test relays to the armature 4 of relay I21. and thence to the winding of relay I25 which now becomes operated. This relay opens the circuits to the selecting magnets which now release.

Due to the release of that selecting magnet which has been operated, relay I34 is released and this closes a circuit at its back contact. to operate relay I26. A circuit s now closed through the contacts on the crosspoint test relays to operate the selecting magnet corresponding tothe link as represented by the trunk veri wh ch a Just pr viously p ra Since contact set II3 has been Operated the link served thereb extends through the contact sets I52and I04 which are undcrthe control of selecting magnet II3. A circuit for this can, therefore, be tracedfrom ground, armature 6 and front contact of relay I33, armature 2 in front contact of relay I31, armature 5 in front contact of relay I21 and thence in a series chain through the armatures 5 and the front contacts of the other operated crosspoint test relays to armature5 of relay I28 thence through the, back contact of this armature to the 0 conductor in thebundle passing through the ten armatures in front contacts of relay I 26, represented armature I of front contact of this relay to the 0 conductor extending to the winding of select: ing magnet H5. Therefore, magnet H6 is again operated to prepare, for the operation of contact set I 92 serving the incoming trunk line. Relay I34 operates and connects ground through the front contact in armature of relay I26, armature 2 and front contact of relay. I33, front contact in armature I of relay II1 to the winding of selector vertical or holding magnet I05. Relay I2 I in the. register circuit is operated at this time through its lower winding but since relay I33 is operated the circuit from the back contact of relay I20.w is open and the off-normal spring of the stepping switch is connected through a contactof relay I21 and front contacts of relay I33 to turn towards normal position where the off-normal contact, opens. When the selector vertical magnet operated the tip and ring conductors from the, selector circuit.

were broken from the line relay I20. which releases. lay IIS releases causing the release of relays H8 and H1 and the register circuit is ready for another call.

If no idle crosspoint is found all of the cross,- point relays will be operated. In this case relay I25 is operated through contacts of the crosspoint relays to. the holding ground of the control circuit. This releases the selecting magnets and the trunk test magnets I35 and I36 without operating trunk magnets such as I29 and I39. Relay I38 i released and the crosspoint test relays now respond to the busy links only thereby operating the selecting magnet cor-. responding to an idle link. The selector ver-. tical magnet is then operated. and the selector is cut through to that link but since the relay I31 is not operated the selector conductors are connected to the busy tone circuit and slow releasing relay I39 becomes up. This releasing relay through its winding and front contact now. supplies battery to the calling subscriber and is therefore under control of this subscriber. When the subscriber in response to hearing the busy tone releases, relay I39 will release and by removing ground from the sleeve. conductor of the incoming trunk will cause the complete release of the selector circuit arrangements.

Figs. 5, 5A and 5B show the connector circuit. Fig. 5 shows the arrangement. of the, crossbar switch. Fig. 5A shows the connector circuits employing this switch and Fig. 5B shows the common controlling circuit used by these various connector circuits.

One six-wire 20-vertical crossbar switch provides the switching mechanism for four connectors and one hundred line terminals. In the arrangement shown, the, horizontals appearing before four verticals are strapped, thus making five groups of four verticals each, one of which verticals in each group is assigned to a given connector. In the case of a trunk hunting connector a 22-vertical switch is used, twenty of which will be wired as just described. The two additional verticals are of the five-wire type and serve to connect the sleeve conductors of all but the last trunk of a PBX group to the unitsstepper to provide for hunting.

In Fig. 5.the contact sets I40, I4I, I44, I45, I48 and I49, are in one horizontal row, and are controlled by the selecting magnet, I52. Likewise contact sets I42, I43, I46, I41, I50 and I5I are in another horizontal row and are controlled by the selecting magnet 53. The horizontal row controlled by the selecting magnet I53 represents the first level and the horizontal row controlled by the selecting magnet I BZ-represents the last level. The contact sets, I40 and I42 represent the first vertical, the contact sets I4l and I43 represent the fourth vertical, the contact sets I44, and I45 representthe seventeenth vertical and the contact sets I45. and I41 represent the twentieth vertical. In accordance with the plan, multiple connections extend from the first connector circuit to verticals I, 5, 9., I3 and I1 and multiple connections extend from the fourth connector to verticals 4, 8, I2; I5 and 23. The contact set I42 represents the first and the contact set I49. represents the last contact set of the first vertical. The horizontal contacts. of the first four verticals are multipled together In due time the first slow-releasing re-,

and extend to twenty lines, the two being served by contact sets I42 and I43 being numbered II and I6 and the two being served by the contact sets I40 and MI being numbered 01 and 06. Likewise the lines served by the contact sets I46 and I41 are numbered 15 and 10 and those served by the contact sets I44 and I45 are numbered 05 and 00. Sleeve connections for the ten trunks in each horizontal extend to the two contact sets at the right, for instance, the sleeves of trunks II, I6, I5 and I6 extend to the contact sets I56 and I5I which connect them temporarily under certain conditions to the ten conductors in the two bundles I54 and I55, which extend to the units stepper.

The numbering of the terminals is thus similar to that of a step-by-step connector, the horizontals representing the levels being selected by the tens digit and the verticals representing the ten terminals per level of the step-by-step switch being selected by the units digit. The numbering of the terminals however is not in consecutive order as is the case of the stepby-step system. These number from 1 to 5 across the level and then repeat for 6 to thus line terminals II and I6 will appear on the left bottom crosspoints while and 00 will appear on the right top crosspoints.

One two-digit register is provided for the four connectors associated with a given switch. The register circuit is arranged to busy back those otherwise idle connectors when engaged. If for traiiic reasons one register is insufficient for four connectors, two or more registers can be used suitably arranged with the connecting relays to the selecting magnets and with blocking means, so that but one connector can be operating the switch magnets at a time.

On a local call the preceding selector connects ground to the sleeve conductor when the selector vertica magnet is operated. This is in advance of the cut-through of the tip and ring conductors and should provide sufilcient time for the operation of the individual multicontact relay of the connector which operates to associate the connector circuit with the common controlling apparatus. Such relays are shown in Figs. 5A as relays I56 and I51. Relays I56 and I51 of the connectors and relay I58 of the register circuit have a non-interfering circuit of the usual type. When relay I58 operates, ground is connected to the sleeve conductors of the idle connectors associated with the same switch. For example when the connector shown in full in Fig. SA has been engaged and relays I 51 and I56 operated then a ground will be extended over the front contact and armature 4 of relay I58 to the sleeve of the first connector, which may be traced through a circuit similar to that extending from armature 3 of relay I58, back contact and armature 2 of relay I66, to the sleeve wire of. the incoming trunk.

When the line relay of the connector, such as relay I59 operates the first slow-release relay I60 is operated in the usual manner and the back contact of relay I59 is then connected through the front contact of armature I of relay I68 and the armature 5 of relay I51 to the left-hand winding of relay 6I6 in the register circuit. The tens register shown schematically beneath relay I6I in Fig. 5B is a magnetic type stepper similar to that shown in Fig. 3A. It is a device which is an electromechanical equivalent of a chain of counting relays and is clearly described in an application Serial No. 389,322, filed April 19, 1941 by George R). Stibitz. Upon the operation of relay I58 a ground connection is extended from armature 2 and front contact of relay I58, through the winding of magnet I63 and thence through the two windings in series of magnet I62 to battery. Magnet I63 is operated but the two windings of magnet I62 oppose .each other and this magnet remains unoperated. The pulsing conductor from armature 5 of relay I51 can, therefore, be traced through unoperated contacts of the tens stepper, the left-hand winding of relay I6I to the connection between the two windings of magnet I62. On the first pulse for the tens digit relay I6I operates and one of the windings of magnet I62 whichis in series with the winding of magnet I63 is short-circuited to release magnet I63 and to operate magnet I62. On the first pulse relay I6I looks through its front contact and armature I to the pulsing conductor. When the pulses for the tens digit cease, relay I6I after an interval determined by its slow-releasing characteristics releases and ground. is connected through the counting contacts of the stepper to operate the selecting mag net of the crossbar switch corresponding to the tens digit. It should be noted that when the magnet I62 of the stepper is energized a contact is closed to energize the right-hand winding of relay I6I. The purpose of this is to reduce the time release requirement of the relay NH.

The release of relay I6I extends the pulsing conductor through its back contact and a winding of relay I64 of the units stepper. The units pulses now step the units stepper through the. proper operation of the magnets I65 and I66. On the sixth pulse an off-normal contact is closed for the operation of relay I61 in the connector circuit which switches the outgoing tip, ring and sleeve conductors of the connector circuit to the mate set of conductors of the crossbar verticals. It should be noted that when the magnet I65 of the units stepper is energized a contact is closed to energize the right-hand winding of relay I64.

The purpose of this is reduce the time release requirements of relay I64.

When the units pulses cease relay I64, after an interval depending on its slow-releasing characteristies, releases and through the counting contacts of the stepper and relay I51.

Upon the operation of relay I64 a circuit is established from ground, armature 2 and front contact of relay I58, through an oil-normal contact closed through the operation of magnet I65 to the armature 2 of relay I64. This results in the operation of relay I68. This is a slow-release relay and after relay I64 releases ground through its contacts operates relay I69 of the connector circuit. It will be noted that relay I58 being operated, a ground is extended over armature 2 and front contact of relay I58 thence through contacts of the stepper controlled by the magnet I65 to armature 2 of relay I 64 and when this releases through the back contact of armature 2 of relay I64, through armature I and back contact of relay I16, thence through the winding of relay I1I to battery and ground. The relay I1I is operated in this circuit and locks to the ground on armature 2 of relay I64. Through its armature I relay I1I extends ground to the armature of relay I68, which remaining operated for an interval after relay I64 releases, now extends ground through armature 3 and front contact of relay I 51 to the lower winding of relay I69 and thence to battery. Relay I69 now connects its upper winding through its front contact and armature 3 to the sleeve of the called line for testing the busy or idle condition.

The vertical magnet is energized and held temporarily through the contacts of the stepper, the contacts of relay Ill and the contacts of relay I51, so that if relay I69 remains operated on a busy condition the holding ground for the vertical magnet being opened at the back contact of armature 4 of relay I69, such vertical magnet will be released after the test. During the busy test, if relay I61 has not been operated, then this connection is through armature 3 and back contact of relay I61 to the sleeve of line numbered 01, by Way of example, and if relay I61 has been operated then this connection is through armature 3 and the sleeve of line 06, by way of example. When relay I68 releases, relay I69 will not release if the line is busy since ground on the sleeve of the called line will hold relay I69 operated through its upper winding. If the line is idle, however, the relay I69 will release and supply holding ground for the vertical magnet. The release of relay I68 in the register circuit operates a relay I12 which causes the release of relays I57 and I58 and this dismisses the register.

The connector circuit shows a relay 13 as a pick-up relay for a two-ring connector. With a one-ring connector relay I13 and the pick-up conductor I14 are omitted.

Upon the operation of relay I317, holding ground from the front contact and armature 2 of relay I60 is extended over armature 4 and front contact of relay I69, the back contact and armature 3 of relay I15, to the winding of relay lie so that when thereafter relay I69 releases the tip and ring conductors are connected to the line and machine ringing is connected through the winding of relay I11. This is the usual ringing and tripping circuit and when relay I11 operates relay I16 releases and relay I18 is operated to reverse battery when the called party answers. When the conversation is completed and the calling party hangs up, 1e first slow-release relay I60 releases in time and restores the circuit to normal.

In case the called line is busy reiay i515 does not release when relay I51 releases. However. the vertical magnet is released and relay I69 is locked to the holding ground through back contact and armature 2 of relay IE1 when that relay releases. Busy tone source connected to conductor I19 is now connected to the ring conductor and will be heard by the calling party. This may be traced from the source of busy tone on conductor I19 through back contact and armature of relay I80, through armature i and back contact of relay I51, front contact and armature 2 of relay I69, condenser ISI, armature I and back contact of relay I80, condenser I82 to the ring of the incoming trunk from the previous selector switch. It may be noted that the three terminals marked T, R, and S included In the bundle I83 are terminals coming from a local selector, whereas the four conductors marked T, R, S and C and included in the bundle I84 are terminals from a toll selector. When the connector is approached over the toll terminals the relay I80 will be operated and a busy tone from a source on conductor I85 will be returned to the calling subscriber in the same manner as that just described.

In the event of a call abandoned before a selection is completed, the release of both the line relay I59 and the first slow-release relay I60 'said sets of contacts and test conductors for said 50 outgoing lines appearing in the contacts of other 7 stepper.

Z 3 1 ifsbb toll train. When ringing is desired application of ground to conductor I86 will operate relay I16 and ringing will proceed as previously described. A call abandoned by the toll operator will cause the release of the register circuit in the manner previously described.

In the showing of Fig. 5B the two relays I10 and HI are provided for trunk hunting purposes When the last units pulse ceases, relay I10 will be operated if connected through the counting con- 20 tacts of the units stepper to a busy PBX trunk.

With relay I10 operated upon the release of relay I64, magnet I65 of the stepper is energized and when magnet I65 releases this energizing circuit is opened at the first contact of the stepper. When magnet I65 again energizes relay I10 operates if connected to the next trunk and if that trunk is busy another step is made by the On idle trunks or the last PBX trunk and on regular lines relay I10 will be released to operate relay I1I as hereinbefore described.

Relay I1I is slow to operate to permit the relay I10 to release and reoperate during the hunting condition. When relay I1I operates connection to the vertical magnets of the connector is completed and the circuit operation proceeds as above described.

What is claimed is:

1. A step-by-step selector comprising an arrangement of coordinately disposed sets of permanently paired contacts, incoming lines each appearing in the contacts of a corresponding number of vertical rows of said sets of contacts, a plurality of links each appearing in the contacts of the horizontal rows of sets of contacts in which said incoming lines appear and in the contacts of a corresponding plurality of vertical rows of said sets of contacts, outgoing trunks appearing in the contacts of the said last vertical rows of vertical rows of said sets of contacts, a selecting magnet for each horizontal row of said sets of contacts, a holding magnet for each vertical row of said sets of contacts, means responsive to impulses incoming over a calling one of said incoming lines for selectively operating said selecting magnets, means for thereafter operating the said holding magnets for the said vertical rows in which said test conductors appear, a

testing circuit accessible to said testing conductors and means responsive to the said operation of said selecting magnet and said holding magnet for operating a holding magnet to cooperate with said operated selecting magnet to operate a set of said contacts to join an idle trunk to an idle link, means for thereafter releasing said operated selecting magnet and said operated holding magnets for said test conductors and said test circuit, and means for thereafter automatically operating a selecting magnet and a holding magnet for operating that one of said sets of contacts in which appear both said selected idle link and said calling incoming line.

2. A dial operated cross bar switch, comprising a coordinately arranged field of sets of permanently paired contacts operated through the temporary operation of one of a plurality of selecting magnets arranged in one coordinate direction and, during the period of operation of said selecting magnet, the operation of one of a plurality of holding magnets arranged in another coordinate direction, incoming lines appearing in a part of said field of contacts, outgoing lines appearing inasecond part of said field of contacts, links for interconnecting said incoming and said outgoing lines appearing in both said parts of said field, means responsive to impulses incoming over one of said incoming lines for selecting a group of outgoing trunks and operating a corresponding one of said selecting magnets, means for thereafter automatically operating one of said holding magnets corresponding to the junction of an idle one of said outgoing lines in the selected group and an idle one of said links, means for releasing said selectively operated selecting magnet, means responsive to the said means for operating said holding magnet for thereafter automatically operating a selecting magnet corresponding to the said selected link and means responsive to the positional appearance of said one of said incoming lines for operating a holding magnet corresponding thereto to interconnect said incoming line and said selected link.

3. A dial operated crossbar switch, comprising a coordinately arranged field of sets of permanently paired contacts operated through the temporary operation of one of a plurality of selecting magnets arranged in one coordinate direction and, during the period of operation of said selecting magnet, the operation of one of a plurality of holding magnets arranged in another coordinate direction, incoming lines appearing in a part of said field of contacts, outgoing lines appearing in a second part of said field of contacts, links for interconnecting said incoming and said outgoing lines appearing in both said parts of said field, means responsive to impulses incoming over one of said incoming lines for successively interconnecting an outgoing line and a link and interconnecting said link and said incoming line.

4. A dial operated crossbar switch, comprising a coordinately arranged field of sets of permanently paired contacts operated through the temporary operation of one of a plurality of selecting magnets arranged in one coordinate direction and, during the period of operation of said selecting magnet, the operation of one of a plurality of holding magnets arranged in another coordinate direction, incoming lines appearing in a part of said field of contacts, outgoing lines appearing in a second part of said field of contacts, links for interconnecting said incoming and said outgoing lines appearing in both said parts of said field, means responsive to impulses incoming over one of said incoming lines for interconnecting an outgoing line and a link and for thereafter interconnecting said link and said incoming line.

5. Switching means for extending one of a plurality of incoming lines to an idle one of a selected group of outgoin lines, comprising a field of sets of permanently paired contacts coordinately arranged, selector magnets each for preparing a row of said contact sets in one direction for operation and holding magnets each associated with a row of said contact sets in another direction for operating prepared sets in said row, incoming lines terminating in part of said field, outgoing lines terminating in a different part of said field, links for extending connections from incoming lines to outgoing lines, means responsive to trains of impulses incoming over said incoming lines for operating a particular one of said selector magnets, means responsive to the operation of said selector magnet for making a busy test of all outgoing lines accessible through the operation of said selector magnet, means responsive to said testing means for establishing a connection between an idle one of said outgoing lines and one of said links and means for thereupon automatically releasing said operated selector magnet and for operating another selector magnet and another holding magnet for interconnecting said connected link and said incoming line.

6. The method of operating a crossbar switch to interconnect a calling line with an idle trunk of a selected group of trunks which consists in selectively operating a selecting magnet thereof corresponding to a desired group of trunks, automatically operating holding magnets to connect a test circuit to the trunks of the selected group, automatically operating the holding magnet corresponding to the junction of an idle link and an idle trunk of the selected group, releasing the said selectively operated selecting magnet and thereafter automatically operating a selecting magnet corresponding to the said selected idle link and a holding magnet corresponding to the said calling line.

SAMUEL B. WILLIAMS. 

